The invention relates to foot pedal devices for controlling engines without the need for a direct mechanical connection between the pedals and the engines. The invention is particularly directed to providing a drive-by-wire system, i.e., driving by electrical or electronic means, rather than by mechanical links.
In the prior art, accelerator pedals are used to mechanically control a vehicle engine and usually include a pedal mounted to a vehicle body with a series of links and levers, or Bowden cables, connecting the pedal to the carburetor, fuel injector, controller, or other similar device. These linkages must be designed to withstand and accommodate engine movements relative to the vehicle frame, as well as to provide accurate control despite such movements. In addition, packaging space must be provided for the linkages to function properly. The space available for routing the mechanical control links, rods, and cables is limited. When electrical sensors are used to monitor the position of the pedal, connection to the carburetor or other engine device can be accomplished with electrical wiring, which is more easily routed through the vehicle.
In drive-by-wire applications, it is important that the pedal system provide the customary feel and performance of a mechanical linkage. The pedals must function responsively to driver input and must provide non-fatiguing resistance. Drivers are accustomed to applying and releasing pressure on a pedal arrangement and become accustomed to the resistance to application of force to the pedal as well as to the rate of withdrawal as the applied pressure is relaxed. With the present invention, the customary feel during the application of force to increase speed and while maintaining speed, as well as the familiar deceleration movement of the pedal can be duplicated in a wire type control.
Typically, the pedal pressure required when advancing the accelerator pedal is greater than that required to maintain a fixed position. This difference is often referred to as a hysteresis effect. This effect is important in maintaining the accelerator pedal in position while driving at a relatively constant speed, and it must also be considered in achieving a desired deceleration time. The pressure which must be applied in accelerating is easily borne but if the back pressure of an accelerator spring produced the same effect during the time it was required to retain or maintain speed it would soon become uncomfortable for the driver to maintain a relatively constant speed. The hysteresis effect provides relief. It lessens the load required to maintain a setting of the accelerator yet there is still force to cause reverse pedal action when the applied pressure is removed.
The hysteresis effect is also important for eliminating undesirable accelerations and decelerations as the vehicle is driven over a bumpy road. Vehicles with manual transmissions do not typically include an accelerator pedal with a hysteresis effect. When the vehicle is driven over a bumpy road, the driver's foot follows the terrain causing the vehicle to accelerate and decelerate, which is undesirable. Thus, hysteresis is needed to provide stability to the vehicle over rough terrain.
Wire type throttle control for vehicle engines with hysteresis generating mechanisms are known. One such example is shown in U.S. Pat. No. 5,408,899. Often these hysteresis generating mechanisms are complex, include a significant number of parts, and are difficult to assemble. The present invention provides an electronic throttle control with an improved hysteresis generating mechanism. The hysteresis generating mechanism is simplified, requires fewer components, and is easier to maintain and assemble than known mechanisms.